This invention relates to an electronic component in which a semiconductor chip is face down mounted on a printed circuit board (hereinafter PCB) by flip-chip bonding, which has satisfactory repairability as well as high connection reliability.
In recent years, direct chip attachment technology such as flip chip bonding has engaged attention. So-called C4 (controlled collapse chip connection) joining is a famous interconnection technology for flip chip bonding in which high-melting solder bumps formed on the chip side are electrically connected to the solder pads formed on a ceramic wiring board.
Where a resin-based circuited substrate, such as an epoxy-glass laminate PCB, is used in flip chip bonding in place of a ceramic circuited board, there arises a poor connection reliability problem because the solder joints are broken due to thermal expansion mismatch between a silicon chip and the resin-based substrate. It is a generally followed practice as a countermeasure against this problem that the gap between a chip and a resin-based circuited substrate is sealed (underfilled) by using a liquid resin composition to diffuse thermal stress and improve reliability.
Thermosetting resin compositions mainly containing an epoxy resin, etc. are generally used as an underfill material. However, thermosetting resin compositions have little repairability or reworkability as an underfill material because, after once cured by heating, they exhibit high adhesion and do not melt, nor dissolve, nor decompose. After underfilling, electronic devices if found defective in electrical interconnection cannot help being scrapped. In the light of the today""s concern of environmental conservation, it is necessary to minimize unrecyclable waste. From this viewpoint, it has been demanded to develop a reworkable underfill material.
An object of the present invention is to provide a electronic component which is repairable if found defective in electrical connection after underfilling.
In order to accomplish the above object, the present inventors have investigated epoxy resin compositions as an underfill material for filling the gap between a PCB and a semiconductor chip. As a result they have found that a liquid epoxy resin composition mainly containing a liquid epoxy resin, a curing agent, and an inorganic filler and having incorporated therein a specific fluorine-containing aromatic diamine compound provides a cured product (sealing resin) that is solvated and subsequently swollen with a specific solvent. The solvent-swollen cured resin film reduces strength and adhesion and becomes capable of being stripped mechanically, thereby enabling repair of the assembly. The fluorine-containing aromatic diamine compound serves to reduce a solubility parameter (SP) of a cured resin because of its trifluoromethyl group or fluorine atom to make a cured resin ready to be solvated and then swollen with a specific solvent. The inventors have ascertained that N,N,Nxe2x80x2,Nxe2x80x2-tetrasubstitution of the fluorine-containing aromatic diamine derivative enhances the solvation and swelling capabilities to an extent enabling reworking.
The present invention provides an electronic component containing a PCB having electrodes for connection and a semiconductor chip having electrodes for connection which is mounted on the PCB with their electrodes facing those of the PCB, the gap between the PCB and the semiconductor chip being filled with a sealing resin layer, wherein the sealing resin layer is formed of a liquid epoxy resin composition comprising (A) a liquid epoxy resin, (B) a curing agent, (C) an inorganic filler, and (D) an N,N,Nxe2x80x2,Nxe2x80x2-tetrasubstituted fluorine-containing aromatic diamine derivative.
It is a preferred embodiment of the invention to use, as component (D), an N,N,Nxe2x80x2,Nxe2x80x2-tetrasubstituted fluorine-containing aromatic diamine derivative represented by formula (I): 
wherein X represents a fluorine atom, CnF2n+1 where n is an positive integer of 1 to 10, or a combination thereof; m represents a positive integer of 1 to 4; and R1, R2, R3, and R4, which may be the same or different, each represents a monovalent organic substituent other than a hydrogen atom. The resin composition containing the derivative of formula (I) exhibits rapid swellability to assure high repairability.
It is a further preferred embodiment of the invention that:
the curing agent as component (B) contains at least one fluorine-containing aromatic diamine compound represented by formula (II): 
xe2x80x83wherein X represents a fluorine atom, CnF2n+1 where n is an positive integer of 1 to 10, or a combination thereof; m represents a positive integer of 1 to 4; R5, R6, R7, and R8, which may be the same or different, each represents a hydrogen atom or a monovalent organic substituent, provided that at least one of R5, R6, R7, and R8 is a hydrogen atom and/or that:
the liquid epoxy resin composition contains a prepolymer resulting from the reaction between at least one fluorine-containing aromatic diamine compound represented by formula (II) and the liquid epoxy resin as component (A).
According to this preferred embodiment, an improved curing rate is obtained. Besides, the state of the epoxy resin composition to be used as an underfill material can be controlled between liquid to paste by using the prepolymer so that a liquid epoxy resin composition can be prepared with ease without involving complicated procedures in the steps of metering and subsequent dispersing.